Modern oil field operations demand a great quantity of information relating to the parameters and conditions encountered downhole. Such information typically includes characteristics of the earth formations traversed by the borehole and data relating to the size and configuration of the borehole itself. The collection of information relating to conditions downhole, which commonly is referred to as “logging,” can be performed by several methods including, but not limited to, wireline or slickline logging, “logging while drilling” (LWD), drillpipe-conveyed logging, coiled tubing-conveyed logging, and tractor-conveyed logging.
One example of a logging tool suitable for use in any of these logging configurations is a dielectric tool. Generally, a dielectric tool includes at least one transmitter and at least one receiver. During logging, the transmitter and receiver abut the adjacent formation and an electromagnetic signal is generated at the transmitter. The electromagnetic signal propagates through the formation such that a portion of the electromagnetic signal reaches the receiver. As the electromagnetic signal propagates through the formation, characteristics of the electromagnetic signal, such as amplitude and phase, change due to the composition and structure of the formation. By measuring the propagation time and changes to the electromagnetic signal's characteristics, an operator can determine properties of the formation through calculation or comparison to previously collected data including, but not limited to, resistivity, permittivity, dielectric constant, water-filled porosity, and water saturation.
The electromagnetic signal is generated by an antenna associated with the transmitter by providing an electrical signal to the antenna. The orientation of the electromagnetic signal produced by the antenna is generally fixed based on the orientation of the antenna and shape of the transmitter housing.
Because formation composition and properties may vary in multiple directions, it is often desirable to collect dielectric logging data using electromagnetic signals in multiple orientations. For example, transmitters having an antenna arranged perpendicular to the dielectric tool axis are sometimes described as operating in “broadside” mode. Broadside mode generally exhibits higher coupling gain and is therefore preferred in lossy logging environments with low resistivity. As another example, transmitters having an antenna arranged parallel to the dielectric tool axis are sometimes described as operating in “endfire” mode and produce an electromagnetic signal perpendicular to that produced in broadside mode. In endfire mode, a dielectric tool determines formation properties primarily in a plane orthogonal to the tool axis. Endfire mode provides greater depth of investigation and is less affected by standoff (i.e., gaps between the transmitter and receiver and the surface of the wellbore caused by a layer of drilling mud or general unevenness of the wellbore surface). Accordingly, a dielectric tool capable of operating in multiple modes is desirable.
While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.